The use of electrical motors to drive tools is well known and widely practiced. Thus, there is commercially available a wide variety of power driven tools, for commercial as well as hobbyist application, for use in construction, shop, and landscaping or gardening applications. For example, it is known to provide electrically driven motors for operating drills, saws, sanders, grinders, hedge trimmers, mowers, and the like. However, it is also known that some electrically operated tools may be hazardous if inadvertently activated. Thus, it is appreciated in the art that safety control switches are necessary to avoid unintended operation of such tools.
It is also appreciated in the art that control switches for electrical motors used to drive various tools may be designed to require coincident operation of a pair of mechanical elements to activate the motor to drive the tool. Such an approach is based on the theory that the likelihood of accidental activation of a tool is minimized by requiring the simultaneous occurrence of two deliberate, intentional, operations. It is contemplated that an accidental event, such as dropping or bumping of the tool, may cause the inadvertent and unintended occurrence of one such operation. However, the likelihood of occurrence of a plurality of required operations, as necessary for activation of such safety control devices, is reduced since a single accidental occurrence is not likely to cause two switch devices to be operated, and particularly to be operated substantially simultaneously.
Yet another aspect of operation of electrical switches for controlling motor driven tools relates to fatigue of the operator in maintaining a tool constantly in an active, or operated, state. That is, on occasion it may be required to operate a tool in a continuously-on state, for lengthy time periods. When an operator is required to exert physical pressure or force against a switch member for a protracted period of time in order to maintain the tool in the continuously-on state, operator fatigue may occur which may result in an unintended deactivation of the motor or, in a worst case situation, may result in hazardous operation of the tool.
Accordingly, it is also known in the art to provide latching mechanisms for locking the tool control switches in a constantly activated condition.
However, various prior art safety and locking devices are cumbersome and require great dexterity on the part of an operator in order to activate or to lock-on the switches. For example, in several such switches it is known to provide a controlling switch on one side of the tool and a separate safety switch on the other side of the tool, and to permit initial operation or locking operation of the switch only when the safety switch is simultaneously operated on the opposite side of the tool. For large tools, such operation may add to the difficulties of operators having small hand-spans, for example.
In another prior art approach, it is known to provide a latch, cooperating with the tool control switch. However, in order to operate the tool or to lock the tool in an active, operated state, the control switch must be depressed in one direction and the latch must be displaced in a direction perpendicular thereto. Again, increased dexterity is required of an operator in order to activate such a safety arrangement.
While these and other prior art approaches do, indeed, perform the function of reducing the likelihood of inadvertent operation of the tool, such prior art approaches also hamper the smooth and unobstructed operation of the tool by an operator.
Still other prior art approaches are known for providing a locking-on function for a tool activating switch. Where a separate button needs to be activated or depressed, simultaneously with operation of a trigger, in order to lock operation in a "constant-on" state, problems similar to those described hereinabove result.
Moreover, the various devices used in the prior art to attain the above-identified functions are needlessly complex and susceptible to failure.